The present invention relates to a hydraulic transmission actuator having piston/cylinder unit in which an actuating piston longitudinally displaceably arranged in the cylinder housing divides the cylinder chamber into at least two pressure chambers which can be acted upon by hydraulic oil by control conduits, and having a piston rod connected with the actuating piston as well as having a sealing element arranged on the actuating piston, by means of which sealing element the two pressure chambers are sealed off from one another.
Hydraulic transmission actuators are used, for example, in the case of automated standard transmissions for synchronizing the transmission gears (see, for example, Johannes Lohmann, “Zahnradgetriebe”, 2nd Edition, Page 156, and on).
In hydraulic transmission actuators of the above-mentioned type, the actuating piston bounded by two pressure chambers is displaced toward the left or right as a result of correspondingly being acted upon by pressure, with a sealing element being provided for sealing off the two pressure chambers on the actuating piston. When using hydraulic transmission actuators, high actuating forces have to be applied, for example, when synchronizing the transmission gears. The actuating forces require a reliable and durable sealing-off and separating of the two pressure chambers.
It is, therefore, an object of the present invention to improve the sealing-off of the two pressure chambers in the area of the actuating piston.
This object is achieved by providing that the diameter of the cylinder housing is locally reduced for increasing the radial contact pressure force of the sealing element with respect to the interior cylinder wall.
For increasing the radial contact pressure force of the sealing element with respect to the interior cylinder wall, the diameter of the hydraulic cylinder is advantageously locally reduced in an area in which high actuating forces act upon the actuating piston.
In a left and right operating position deviating from the center position of the actuating piston in the hydraulic cylinder, the diameter of the hydraulic cylinder is reduced in comparison to the diameter of the hydraulic cylinder in the center position of the actuating piston. As a result, in both operating positions of the actuating piston, a higher contact pressure force of the sealing element is achieved with respect to the interior cylinder wall.
The diameter of the hydraulic cylinder widens after passing through both operating positions, so that the contact pressure force of the sealing element with respect to the interior cylinder wall is adapted to the reduced actuating forces.
As a result of the fact that the actuating piston and, therefore also, the cylinder housing have a stepped construction, in a first adjusting path with a small piston diameter, a high adjusting speed can be achieved with low friction, while, in the two operating positions, the hydraulic force acts upon the large piston diameter, so that a higher radial contact pressure force of the sealing element against the interior wall of the cylinder housing can be generated.
The hydraulic transmission actuator can be used particularly as an actuating element for synchronizing transmission gears in the case of automated standard transmissions.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.